
- Java.util包类
- Java.util - 首页
- Java.util - ArrayDeque
- Java.util - ArrayList
- Java.util - Arrays
- Java.util - BitSet
- Java.util - Calendar
- Java.util - Collections
- Java.util - Currency
- Java.util - Date
- Java.util - Dictionary
- Java.util - EnumMap
- Java.util - EnumSet
- Java.util - Formatter
- Java.util - GregorianCalendar
- Java.util - HashMap
- Java.util - HashSet
- Java.util - Hashtable
- Java.util - IdentityHashMap
- Java.util - LinkedHashMap
- Java.util - LinkedHashSet
- Java.util - LinkedList
- Java.util - ListResourceBundle
- Java.util - Locale
- Java.util - Observable
- Java.util - PriorityQueue
- Java.util - Properties
- Java.util - PropertyPermission
- Java.util - PropertyResourceBundle
- Java.util - Random
- Java.util - ResourceBundle
- Java.util - ResourceBundle.Control
- Java.util - Scanner
- Java.util - ServiceLoader
- Java.util - SimpleTimeZone
- Java.util - Stack
- Java.util - StringTokenizer
- Java.util - Timer
- Java.util - TimerTask
- Java.util - TimeZone
- Java.util - TreeMap
- Java.util - TreeSet
- Java.util - UUID
- Java.util - Vector
- Java.util - WeakHashMap
- Java.util包额外内容
- Java.util - 接口
- Java.util - 异常
- Java.util - 枚举
- Java.util有用资源
- Java.util - 有用资源
- Java.util - 讨论
Java集合frequency()方法
描述
Java集合frequency(Collection<?>, Object) 方法用于获取指定集合中等于指定对象的元素个数。
声明
以下是java.util.Collections.frequency() 方法的声明。
public static int frequency(Collection<?> c, Object o)
参数
c − 这是用于确定o频率的集合。
o − 这是要确定其频率的对象。
返回值
NA
异常
NullPointerException − 如果c为null,则抛出此异常。
整数列表中元素出现次数计数示例
以下示例演示了Java集合frequency(Collection,Object)方法的使用。我们创建了一个包含一些整数的List对象,并打印了原始列表。使用frequency(Collection, T)方法,我们打印了特定元素的计数。
package com.tutorialspoint; import java.util.ArrayList; import java.util.Arrays; import java.util.Collections; import java.util.List; public class CollectionsDemo { public static void main(String[] args) { List<Integer> list = new ArrayList<>(Arrays.asList(1,2,3,3,5,3)); System.out.println("Initial collection value: " + list); // print the frequency of 3. int result = Collections.frequency(list, 3); System.out.println("3 is present: "+result + " times."); } }
输出
让我们编译并运行上述程序,这将产生以下结果:
Initial collection value: [1, 2, 3, 3, 5, 3] 3 is present: 3 times.
字符串列表中元素出现次数计数示例
以下示例演示了Java集合frequency(Collection,Object)方法的使用。我们创建了一个包含一些字符串的List对象,并打印了原始列表。使用frequency(Collection, T)方法,我们打印了特定元素的计数。
package com.tutorialspoint; import java.util.ArrayList; import java.util.Arrays; import java.util.Collections; import java.util.List; public class CollectionsDemo { public static void main(String[] args) { List<String> list = new ArrayList<>(Arrays.asList("A","B","C","D","C","C")); System.out.println("Initial collection value: " + list); // print the frequency of C. int result = Collections.frequency(list, "C"); System.out.println("C is present: "+result + " times."); } }
输出
让我们编译并运行上述程序,这将产生以下结果:
Initial collection value: [A, B, C, D, C, C] C is present: 3 times.
对象列表中元素出现次数计数示例
以下示例演示了Java集合frequency(Collection,Object)方法的使用。我们创建了一个包含一些字符串的List对象,并打印了原始列表。使用frequency(Collection, T)方法,我们打印了特定元素的计数。
package com.tutorialspoint; import java.util.ArrayList; import java.util.Arrays; import java.util.Collections; import java.util.List; public class CollectionsDemo { public static void main(String[] args) { List<Student> list = new ArrayList<>(Arrays.asList(new Student(1, "Julie"), new Student(2, "Robert"), new Student(3, "Adam"),new Student(1, "Julie"))); System.out.println("Initial collection value: " + list); // print the frequency of Julie. int result = Collections.frequency(list, new Student(1, "Julie")); System.out.println("Julie is present: "+result + " times."); } } class Student { int rollNo; String name; Student(int rollNo, String name){ this.rollNo = rollNo; this.name = name; } @Override public String toString() { return "[ " + this.rollNo + ", " + this.name + " ]"; } @Override public boolean equals(Object obj) { Student s = (Student)obj; return this.rollNo == s.rollNo && this.name.equalsIgnoreCase(s.name); } }
输出
让我们编译并运行上述程序,这将产生以下结果:
Initial collection value: [[ 1, Julie ], [ 2, Robert ], [ 3, Adam ], [ 1, Julie ]] Julie is present: 2 times.
java_util_collections.htm
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